1. Technical Field of the Invention
The present invention relates to a cosmetic or dermatological composition for topical application, in particular for photoprotecting the skin and the hair, comprising, in a cosmetically acceptable support:                (a) at least one dibenzoylmethane derivative,        (b) at least one 1,3,5-triazine derivative that is photosensitive in the presence of a dibenzoylmethane derivative, and        (c) at least one 4,4-diarylbutadiene compound; the weight ratio of the 4,4-diarylbutadiene compound to the dibenzoylmethane derivative being greater than 2.5 and said composition characteristically containing no cinnamate derivative.        
This invention also relates to a process for improving the photostability of a 1,3,5-triazine derivative that is photosensitive in the presence of a UV-screening agent of the dibenzoylmethane derivative type, which entails formulating with the triazine derivative/dibenzoylmethane derivative combination an effective amount of at least one 4,4-diarylbutadiene compound.
2. Description of Background/Related/Prior Art
It is known that light radiation with wavelengths of between 280 nm and 400 nm permit tanning of the human epidermis and that light rays with wavelengths more particularly between 280 and 320 nm, known as UV-B rays, cause skin burns and erythema which can harm the development of a natural tan. For these reasons, as well as for aesthetic reasons, there is a constant demand for means of controlling this natural tanning in order thus to control the color of the skin; this UV-B radiation should thus be screened out.
It is also known that UV-A rays, with wavelengths between 320 and 400 nm, which cause browning of the skin, are liable to induce adverse changes therein, in particular in the case of sensitive skin or skin which is continually exposed to solar radiation. UV-A rays cause in particular a loss of elasticity of the skin and the appearance of wrinkles leading to premature aging of the skin. They promote triggering of the erythemal reaction or amplify this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as the conservation of the skin's natural elasticity, for example, an increasingly large number of individuals wish to control the effect of UV-A rays on their skin. It is thus desirable also to screen out UV-A radiation.
In this respect, one particularly advantageous family of UV-A screening agents currently consists of dibenzoylmethane derivatives, and in particular 4-tert-butyl-4′-methoxydibenzoylmethane, which have high intrinsic absorbing power. These dibenzoylmethane derivatives, which are products which are now well known per se as screening agents that are active in the UV-A range, are described in particular in FR-A-2-326,405 and FR-A-2-440,933, as well as in EP-A-0-114,607; 4-tert-butyl-4′-methoxydibenzoylmethane is moreover currently sold under the trademark “Parsol 1789” by Hoffmann LaRoche.
1,3,5-Triazine derivatives are particularly desired in antisun cosmetics due to the fact that they are highly active in the UV-B range, and even in the UV-A range for some of these compounds depending on the nature of the substituents involved. They are especially described in patent applications U.S. Pat. No. 4,367,390, EP-863,145, EP-517,104, EP-570,838, EP-507,691, EP-796,851, EP-775,698, EP-878,469 and EP-933,376, and the following are known in particular:                2,4,6-tris[p-(2′-ethylhexyl-1′-oxycarbonyl)anilino]-1,3,5-triazine or “Ethylhexyl Triazone” (INCI name), sold under the trademark “Uvinul T 150” by BASF,        2-[(p-(tert-butylamido)anilino]-4,6-bis[(p-(2′-ethylhexyl- 1′-oxycarbonyl)anilino]-1,3,5-triazine or “Diethylhexyl Butamido Triazone” (INCI name), sold under the trademark “Uvasorb HEB” by Sigma 3V. They have high UVB-absorbing power and it would therefore be very advantageous to be able to use them in combination with 4-tert-butyl-4′-methoxydibenzoylmethane mentioned above with the aim of obtaining products that afford broad and effective protection against all UV radiation.        
EP-0-967,200, DE-197,46,654, DE-197,55,649, EP-1-008,586, DE-100,07,017, EP-1-133,980 and EP-1-133,981 disclose antisun compositions based on 4,4-diarylbutadienes, which may contain other additional screening agents, for instance the dibenzoylmethane derivatives and the triazine derivatives as mentioned above.
However, it has now been found that certain of these 1,3,5-triazine derivatives are photosensitive when they are in the presence of 4-tert-butyl-4′-methoxydibenzoylmethane, i.e., under UV irradiation, they have the drawback of undergoing substantial chemical degradation. Under these conditions, the combination of the two screening agents no longer affords prolonged, broad antisun protection to the skin and the hair.